Role of Autophagy in the Antitumor Activity of Aloin in Breast Cancer Cells

Abstract

Aloin is a natural bioactive anthraquinone extracted from Aloe sp. and has the potential of tumor regression by inhibition of cell proliferation and induction of cell apoptosis in different human cancer cell lines. The ability of cancer cells to evade apoptosis, which often limits the efficacy and accounts for the resistance to chemotherapy, strives the search of autophagy process as an alternative target to promote cell death. The present study was undertaken to verify the autophagy process as a probable mechanism for the antitumor activity of aloin in 2 types of breast cancer cell lines; estrogen receptor positive (T47D) and triple negative (MDA-MB231), compared to an anthraquinone analog, doxorubicin. Initially, the cytotoxicity of increasing concentrations of aloin and doxorubicin were assessed using MTT and clonogenic assays at 2 exposure periods (24 and 72h) to determine the half maximal inhibitory concentration (IC50) of aloin and doxorubicin in both types of cell lines. The formation of autophagy process in the treated tumor cells was initially detected by using transmission electron microscope (TEM). Emphasis of autophagy process was then achieved by monitoring the formation of acidic vesicular organelles (AVOs) qualitatively by confocal fluorescence microscope, and quantitatively by fluorescence activated cell sorting (FACS). Finally, the protein expression levels of some